Charging and discharging means for end-loading transit mixers



g- 7, 5 w H YANTES ETAL' 2,563,770

CHARGING AM DISCHARGING MEANS FOR END-LOADING TRANSIT MIXERS' Filed Jan. 5, 1950 3 Sheets-Sheet l Figi l l lllmlw ss BY Clarence I. Bohmer.

Eu ne Bqrkzr? A TTOR/VEK g- 1951 w H YANTES ET AL 2,563,770

CHARGING ANI J DISCHARGING MEANS FOR END-LOADING TRANSIT MIXERS Filed Jan. 5, 1950 3 Sheets-Sheet 2 INVENTORS W||||am H.Yan1'es. BY Clarence LBohmer.

ugene Barkgr: M l WW FWLJFU rap/v5):

g- 1951 w. H. YANTES ET AL 2,563,770

CHARGING AND DISCHARGING MEANS FOR END-LOADING TRANSIT MIXERS Filed Jan. 5, 1950 3 Sheets-Sheet 5 JNVENTORSY Wilhom H. Yanfzs. BY Clarence LBohmer.

Eugzne Bar-ken W rm-mb Patented Aug. 7, 1951 CHARGING AND DISCHARGING MEANS FOR END-LOADING TRANSIT MIXERS William H. Yantes, Clarence I. Bohmer, and Eugene Barker, Columbus, Ohio, assignors to The Jaeger Machine Company, Columbus, Ohio, a

corporation of Ohio Application January 5, 1950, Serial No. 136,858

17 Claims. i (01. 259161) Our invention relates to charging and discharging means for an end-loading transit mixer. It has to do, more particularly, with a charging and discharging device which is mounted at the open upper end of the inclined drum of a transit mixer of the high-dump type.

Many arrangements of charging and discharging devices for transit mixers of the high-dump type have been provided in the prior art. One type of device comprises a loading hopper mounted for movement between a charging position, where it is associated with the end opening, and a discharging position, where it is spaced from the opening. In this type of device, an annulus or door has been provided between the inner or lower open end of the hopper and the drum opening. This annulus is connected to the lower end of the hopper by sealing means, which permits relative rotation, so that pressure can be applied to the hopper to move it into charging position where the annulus will seat around the drum opening and will be pressed so firmly thereagainst that it will rotate with the drum. The hopper is usually carried or guided by a centrally disposed shaft which extends through the drum opening, the annulus, and the hopper, and this interferes with proper feeding ,of material through the hopper and annulus and through the opening. Usually the closing force for the door orannulus is applied at angularly spaced points at its circumferential edge, requiring complicated actuating means and not always applying even pressure around the door and permitting it to seat properly. Another difiiculty with prior art devices of this general type, is the provision of an effective seal between the outer or upper end of the relatively rotatable annulus and the inner or lower end of the hopper. This is especially difiicult, due to the fact that the pressure required for seating the lower or inner end of the door or annulus around the drum opening is usually applied through the seal between the hopper and the annulus. If the seal is the usual compressible gasket type between two relatively rotatable surfaces, the abrasive fine material, of the material to be mixed and the mixed material, will work between such surfaces and in a very short period destroy the seal.

One of the objects of our invention is to provide a charging and discharging device mounted at the drum opening of a high-dump mixer, the device including a hopper mounted for movement between charging and discharging positions relative to the drum opening, an annulus or door being provided between the inner open end of the hopper and the drum opening, novel means being associated with the hopper for easily and quickly moving it between charging and discharging positions relative to the drum opening.

Another object of our invention is "to provide means for mounting the hopper and associated annulus or door for movement between charging and discharging positions which is of such structure that the mixer drum opening, the annulus, and the hopper will be completely unobstructed so as to facilitate movement of material therethrough.

Another object of our invention is to provide a device of the type indicated wherein the means for moving the hopper between its charging and discharging positions is so designed that a minimum amount of eifort will be required by the operator of the mixer to move it between its two positions.

Still another object of our invention is to provide means in association with the moving means for ensuring that resilient pressure Will be applied on the annulus through the hopper, when the annulus is seated around the drum opening, to ensure that an effective resilient seal will be provided at this point.

Another object of our invention is to provide a device of the type indicated wherein the means for moving the hopper and the door between charging and discharging positions applies its pressure at a single point substantially at the center of the hopper to ensure that uniform pressure is supplied at all points around the annular door which also is inherently resilient, thereby ensuring proper seating of the door around the opening.

A further object of'our invention is to provide novel sealing means between the relatively rotatable annulus and hopper which is so designed that there will be little danger of abrasive materials working between the relatively rotatable sealing surfaces and which is so designed that even though the thrust force, for seating the annulus or door around the drum opening, is applied through the sealing means, there will be no compression on the flexible sealing member associated with the sealing means which will eliminate the necessity of frequent removal and replacement of such flexible member.

Various other objects will be apparent.

According to our invention, the hopper is pivoted to an extension of the'mixer frame adjacent the drum opening for swinging movement in a vertica1 plane. The hopper carries the annulus or door on its lower open end and is swingable from a charging position, where the inner or lower edge of the annulus is seated around the drum opening, to a discharging position, where the said edge of the annulus is spaced from the opening. No central support or guide is necessary for the hopper and, consequently, the hopper, door and drum opening are unobstructed. The annulus is rotatably mounted on the hopper e 3 by means of a novel sealing joint provided between the. upper or outer edge. of the annulus and the lower or inner edge of the hopper. For swinging the hopper between its two positions, an actuating unit is connected to an extension of the -mixer frame and to the rear side of the hopper for supplying actuating pressure to the hopper substantially at its center. This unit. can be 'con-. trolled to quickly move the hopp r and. the annulus carried thereby between its two. positions. When the annulus is moved into sealing position around the drum opening, the actuating unit ap plies thrusting pressure through, the hopper and onto the annulus to properly seat it; Obviously, this pressure or thrust is also applied through the sealing joint between the. hopper and the annulus butthis joint iS.S,o, designedthat this pressure will not produce excessive. wear onv the sealing joint and will not interfere with relative. rotation of the. annulus and the hopper. The actuating unit has resilient means. associated therewith which will ensurethat. resilient pressure will always be.- applied on the. annulus when it is seated around the opening. Therefore, although an actuating unit is provided for positively moving. the hopper and annulus into charging position, the unit will yield as the annulus is-forcedon its. seat and this, will compensate for any build-up. of material on such seat.

The preferred embodiment, of our invention'is, illustrated in the accompanying drawings wherein. similar characters of. reference designate corresponding parts and wherein Figure l is a side'elevational, view illustrating our device appliedv to a transit mixer of the high.- dump type.

Figure 2 is an enlarged view showing. how the device is supported at the end of. the mixer and showing it in discharging position.

Figure 3 is,'a. detail, partly in elevation, and. partly in longitudinal section, illustrating a hy-- 4' elevation and partly in section of the mechanical actuating unit of our device.

Figure 14 is a sectional view taken. substantially along line l4'|4 of Figure 15 through the handwheel control mechanism for the actuating unit of Figure 13.

Figure. 15,. is. a sectional view taken substantially along the line l5-I5 of Figure 14.

With reference to the drawings, in Figures l, 2 and 4 we have illustrated the general arrange-'- ment of the charging and discharging device which. We provide inassociation with the mixer.

The mixer includes the rotatable mixer drum 10 which is disposed in rearwardly and upwardly inclined position on a frame indicated generally by the numeral I l. The; charging and dischargingv device ofv our invention is illustrated enerally by the numeral I2 ancl'is"v carried at. the.

rear or upper end ofithe. druinil [I by means of an upstanding extension [3 of the frame llf.' The.

. mixer drum [I], as shown best in Figure 7,;i's proedge to the extension l3 of the, mixer, frame... It. will be noted from Figures 1, 2 and. that the.

draulic actuating unit which. may be provided. on, H

details of the hydraulic unit, such unit being in.

condition to move the hopper into. discharging position. a

Figur Bis a vertical sectional view through the hydraulic unit. and]v showing it in conditionhto' move the hopper into charging position.

Figure '7 is an enlarged detail mainly in vertical sectionand illustrating, mainly the sealing. joint between the annulus or door and the hopper and the seat around the drum opening for the.

annulus.

Figure 8 is anenlarged vertical sectionalview.

through the. sealing joint between the annulus.

and the hoppe Figure 9 is a view similar to Figure '7v but showing a fiat surface rather than the tapering one of Figure '7.

Figure 10 is a view similar to Figure 7 but showing another. modification of the sealing joint between the annulus or. door and the hopper and the seat around the drum opening for the annulus.

Figure 11 is a. sideelevational view of our device with a mechanical actuating unit rather than a hydraulic actuating unit associated. therewith.

Figure 12 is an enlarged. detail in plan of part of the actuating unit of Figure 11.

Figure 13 is anenlarged detail partly in sid vided with the opening Mat. its; rear or upper I end through which material may passijAring" I5 is disposed in surrounding relationship to this.

opening. I' l andis provided with an. inclined". cult.-

wardly extending flange [521 which supports. a finished ring door seat I16 for the opening [4; The seat It is welded. to the flange, l'5ajj Our device l2 includes a hopper. CT, the upper end it. of which may be. open or may bepro'vided with a suitable closure. The reariwall' 1'9 of the hopper is inclined. downwardly and. forwardly sothat material deposited in the upper enclzthereof, will flow downwardly'therethrough by gravity. f

The hopper is pivoted. at. its forward and. upper.

forward wall [901, of the hopper is provided with.

forwardly extending pivotarmsi'fl at itsoplpositle.

sides. These arms carry bearings 21? at their forward ends which are rotatably disposed on a transverse rod 22; This rod. is carried; in, sleeves 23. which. are supp'ortedonthe. upjper. endsiof up.-

' standing brackets 2. 31 The. brackets 24 rest upon and are secured to the upper ends of large. triangular shape supporting' member 25 which may be welded. or otherwise secured. to the forwardly leaning. extension, E3 of the mixerfra'me.

swung about the axis of of thepivot rod 22;

The forward or lower end o'fth'e hopper is open and carries a rotatable annulus or" door 26'. in association. therewith which. is disposed between the drum It and hopper 12. The annulus 2'6 mounted on the hopper, in. such a; manner'that relative rotation therebetween is, permitted means of a special type of sealing joint indicated? generally by the'numeral 2T. vThis/joint is; illustrated' best, in Figures? and 85.

The lower openend of. the vlioppierlis.provided. with a ring 28. which. may, be. welded thereto around. the opening. thereof: This ring 23 is provided with anoutwardly extending, flange 29 at its rear edge which may be fjorm'e'dpasj apart thereof. or. welded thereto. Ah'eadlofthe' flange 29 and in contact therewithiis a. thrustiring 30,

which. issecured to the; flange' 2,9,' preferably removably, for rotation. therewith; The. inner edge of this. thrust. ring has. at forwardly extending lip 3!.

around the ring. 2.8.and may be. secured thereto,

for example by'weldingu Thisringil isgp'rovidedi with anoutvvardly. directedfiange fi. whijchhas. a.

beveledouter edge= ,-34; Thepartsofithe sealing Thus; it will" be apparent that the; hopper IT can be,

Just ahead. of. the forward. edge} of. the, lip" 3 an axially extending. ring 32. is. disposed.

ried by the hopper. It will be noted from Figure 8 that the rear surface of the ring 30 and the inner edge thereof are machined to provide a lube ricant-receiving space 35 to which lubricant can be fed by pressure fittings 36. It will also be noted that a substantial space 31 is provided between the ring 39 and flange 33.

The annulus 26 is provided at one edge with an inwardly extending flange 38 which is disposed at a suitable angle so that it will be parallel to the flange '29 on the hopper. The flange 38 is so positioned that it extends into the space 31 and its inner edge 39 tightly contacts the outer side ofllip 3|. Secured to the forward side of the flange 38 is a flexible sealing ring 49 which is preferably made of rubber. This ring is secured in face contact with the flange 38 by means of the removable screw bolts 4-! which carry collars 42 that press against sealing ring 40. The inner edge 43 of the flexible ring 49 will bear against the beveled surface 34 on flange 33. As indioated, when the ring 40 is drawn tight against flange 38, the outer edge 43 of the flexible ring will bend and will resiliently contact beveled surface 34. The other edge of annulus 26 is adapted to seat on the seat I6 provided around the drum opening and when moved into association therewith will be angularly disposed relative thereto as indicated to ensure proper sealing contact. When the annulus 26 is pressed against the seat 16, it will rotate with the drum, relative rotation between it and the hopper being permitted by the sealing joint 21. The flange 38 on member 26 will merely rotate in the space 37 between flanges 30 and 33 and at the same time the edge 43 of the flexible sealing ring 40 will rub against the beveled surface 34 and will maintain sealing contact therewith. The lubricant will also pass between flange 33 and flange 38, as indicated in Figure 8, and will build up pressure therein which will tend to prevent fines from entering between flexible edge 43 and beveled surface 34 and reaching the relatively rotatable metal sealing surfaces on members 30 and 58.

For moving the hopper ll about the pivot axis 22-, we provide the unit illustrated generally by the numeral 45 in Figures 1, 2 and 4. This unit is supported by means of a yoke 46 which extends around the rear side of the hopper and is spaced rearwardly therefrom. The arms 4'! of this yoke may extend forwardly along each side of the drum ID to the forward end of the drum where they may be suitably anchored to the frame II. The arms 41 are rigidly bolted at 48 to the frame extension l3 and at 49 to the triangular members 25.

The unit 45 is shown in detail in Figures 5 and 6 and comprises a supporting sleeve 59 which has trunnion bolts 5| carried at its forward and lower end which are rotatably disposed in openings formed in the forward and upper ends of arms 52. These arms 52 have their rear ends welded as at 53 to the transversely extending part of the yoke 46 and extend upwardly and forwardly therefrom. Thus, the sleeve 50 is free to pivot about an axis passing through the trun-. nions 5|.

Supported by the sleeve 50 for limited axial movement relative thereto is a hydraulic cylinder and piston unit 55. This unit comprises the cylinder 56 which is slidably mounted in an opening provided in a bearingplate 51 which is secured to the forward end of sleeve 5|]. Disposed within the cylinder 56 is a piston 58. This piston 58 is mounted on a piston rod which includes the forwardly extending section 59 and the rearwardly extending section 60 which are coupled together at 6|. The section 59 is mounted for axial sliding movement in a bearing 62 disposed at the. forward end of cylinder 56 while the section 56 is similarly mounted in'a bearing 63 provided at the rear end of cylinder 56. This bearing 63 is provided with a tubular extension 64 which extends. rearwardly through an opening provided in a bearing plate 65 secured to the rear end of cylinder 56 and in which it can move axially. Surrounding the extension 64 and disposed between the plate 65, on the rear end of cylinder 56, and an inwardly. turned flange 66, on the rear end of sleeve 50, is a compression spring 61. It will be noted that the .bearing extension 64 extends through the opening 66u within flange 66 and is axially movable therein and that it carries on its outer end lock nuts 68 which are threaded thereon. Nuts 68 serve as a stop for cooperating with the flanged end. 66 of sleeve 59 to limit forward movement of cylinder 56. The forward end of the section 59 of the piston rod is coupled at 69 to the rear end of a connecting pin 19 which carries a clevis .H at its forward end that, in turn, is pivoted at 12 to a lug '13 on the back wall IQ of the hopper: A flexible sleeve 14 preferably encloses the coupling 69.;

It will be noted that each bearing 62 and 63 is provided with a chamber 15 surrounding, the associated section of the piston rod for receiving the hydraulic fluid. Associated with each of these chambers and leading thereto is a line 16. Exhaust of fluid from one end of the cylinder and supply of fluid to the other end is controlled by means of the usual reversible valve 11 which is connected to the lines 16 and to a suitable source of hydraulic fluid under pressure. The valve 11, of course, is preferably located at the rear side of the mixer.

With the valve 11 in one position, the piston 58 will beat therear end of the cylinder 56, as shown in'Figure 5. This pulls the piston rod rearwardly and swings the hopper rearwardly and upwardly about the pivot axis 22. In this position, as shown in Figure 7, the annulus 26 will be spaced'from its seat l6 and discharge of material through the opening [4 and down through the indicated space will be permitted. At this time the various parts of the sealing joint 21 between the hopper and annulus will be in proper association but will be under no thrust. The spring 6! will be exerting no force on the end of the cylinder 56.

When it is desired to move the hopper and annulus into charging position, the valve ll'i is operated to reverse the flow of hydraulic fluid, as indicated in Figure -6. This will move the piston 58. forwardly and downwardly and the cylinder until the annulus 26 engages seat [6. The continued hydraulic pressure causes the cylinder 58' to moverearwardly and press against the spring 61. The spring-will be sufficiently strong to resist compression to any considerable extent and the piston 58 will serve to press the annulusfirmly butresiliently on its seat l6. Thus, the initial movement of the piston 58 will seat the annulus and then spring pressure is applied by the cylinder 56 being forced against the spring 61. This action continues until full forward travel of the piston in the cylinder is accomplished.

It willbe thusapparent that before the piston reaches the extentof its forward travel, a re-.

silient pressure or thrust is applied to seat the door or annulus 26 and this makes it unnecessary to accurately determine thefoirward" travel of the piston. Also, it ensures proper-seating of. the annulus or door even though material buildsup on the seat I6? Although the thrustpressure for seating the annulus ordoor at the drum openi-i ing is applied through the sealing-joint 21, this willhave, no deleterious-effect on the seal dueto the fact that the thrust-is: applied'by ring 30. on: flange 38 and has no effect on the fie'xiblerin 410 Furthermore; relative rotation is permitted and the seal will be maintainedby the flexible edge 43 of ring fill-wiping the bevel surface 34. It will benoted that the force for moving'the hopper between its various positions: is applied at the center of, the hopper which makes it possible to provide a simplified actuating structure and also ensures that uniformseating pressure will be ap plied all around the door 16;

The annulus or door member 26 need not be of the particular form shown in- Figure 7 butm'ay be of other forms, for example, a flat form, as i'ndtcated in Figure 9, where theannulusis: desig nated 26b;

Figure 10 shows: still afurtherform: of tapered a clevis- 12a. The rear and upper end of this bar annulus or door member zficwhichcontacts with a flat ring seat I60; This seat Ilia is bolted to the flange l5b-rather'than welded as-shown in Figures '7, 8' and 9. The form: shown Fig ure 7 and the formsshown inFiguresQ and 1 0are for illustrative purposes" only and the door or annulus may'assume other'formsl- The actuating unit previously described" is fluid-operated, preferably" hydraulically operated. However, as shown iniFig-uresl1 to-1-5,'i'n-' elusive, a mechanicalactuating unitmaybe pro vided.

In this structure-the hopper: l-Ja is carried onthe mixer substantially as-befo're. The pivot arms 20a on the hopper arepivoted" to the brackets 24a at the horizontal pivot. 2200; In this instance, the brackets 24a are adjustably carried by the upstanding supporting members 25a. IIhe brackets 24a are normally clamped to the mem bers 25a by clamping bolts 241) which: pass through. openings and slots in the cooperating members 24a and 25a; Adjustable-screws 2511' are connected-to the brackets 24a, andmembers 25a and may be used for adjusting 'thebracketsforwardly or rearwardly on= members '25a...when the=bolts24b are released. This provides-means for adjusting the pivot axis 22d ofethe hopper forwardly or rearwardly. Ifnecessary; the bolts 241). can be released and shims positioned-between members 24a andl 2 5a to: vary therheight' ofthe pivot 22a. Thus, the location of the pivot 220; can be adjusted accurately: relative to thefmi'xer drum I On to accurately position door Raf-relative to the drum opening and thentheboltsflb can be tightened.

The support for theunit 45a' comprises a yoke. dfiaxwhich extends rearwardlytaroundithenhopper and has its forward: ends anchoredito the plates 25a by means of brackets "a. For bracing-the rearend of the member 46a,the-rearwardly'and upwardly extending. braces 48a are provided.

which. have theirlower' ends bolted 'at 48b to members 725a at' the lower ends thereof-and: their upper ends boltedzto braoketscfld whichiextend rearwardly and upwardly from? the curved part of, supporting. member. 46a to 'which they" are welded. Thus, the rearwardlyextending:member 46a will berigidlybraced: I

The. unit 45a is a toggle 'uniti and issupported by themember 46a; It includeslatoggle'shaft Ella which extends transversely and which is supported at' its ends for rotation in the'brackets 48d" andiwhich' is supported intermediate itsi ends'by the: forwardly and upwardly extending arms 5211 which have their rear ends welded to member 46a substantially midway between the ends thereof; An actuating rod 59a is'provided and this rod is pivotally connected for vertical swinging movement to the rear side of the hopper Ila, substan-' tially at: the center of the hopper, by means of 59a is enlarged and is provided witha longitudinally extending guide slotf59b through which the" toggle shaft 5m passes. The-forward portion of the bar 59a: is reduced and slidably mounted on this reduced portion of the bar is acollar50a; Infront ofthis collar 50a is a compression spring 67a which surrounds the reduced part of the bar 59a and: which engages a fixed collar 65a mounted at the forward end of the bar. The rear end or the spring 67a fits into a cup 5% formed within member 5021 at the forward side thereof. This spring normally tends to keep member SDa rearwardly' in engagement with the shoulder 50b formed at the beginning of the enlarged rear portion of the bar 59a. 7

Connected to the collar 50a at diametricallyopposedpivots are the toggle" links 81 which are of substantially L-shape, as shown in Ffig ure 13. Theseli'nks are rigidly connected together by a transverse: bolt 82 located behind; collar 56a. The rearends of these links are pivoted at 83*to the forwardends of toggle levers 84- which are keyed on the transverse toggle shaft 5m at opposite'sides of members 52d;

The shaft 5m may berockedin order torock the toggle levers '84 about the axis of such shaft by means of a rocker arm 85-keyed on one end thereofm This arm is rocked by means of abar 16a which has its upper end pivoted thereto at 86 and which has its lower end connected to a handwheel-control Ha.

The unit- 'Ila' includes the hand'wheel 81 which iskeyed to the outer end of shaft 88- that isro tatably mounted in a transverse bearing 89- mounted in a vertically supporting plate 90 at the rear of themixer framebelow one of the'members 25a. The plate SID-carries a bracket 9! which extends laterally outwardly therefrom and on which is supported a plunger 'latch- 92- that cooperates with notches 93'' in the hub 94* of the handwheel' 81-. The plunger latch 92 can be-with'- drawn topermit rotation of the handwheel and,

whenreleased; will automatically lock'the handwh'eel'in fixed position; 7

The inner end ofthe-shaft 8'8 carries a pinion- 95" which is keyed therein and whi'ch meshes with an internal gear 96 that is keyed-on atransverse stub shaft 9-! which is parallel to shaft 88- and is rotatably mounted in abearing 91a carried-by theplate 90. The outer end of the shaft 91 has} a stop arm 98 keyed th'ereon while the inner endhasa crank-arm 99 keyed thereon which is piv-- oted'at I90 to the lower end-of the bar 76a;

It will be apparent that when latch 92 is released; the handwheel" 81 can be rotatedand this Will rotate the-stub shaft 91. This will swing the arm 99 and exert a pushor pull on the-bar 16a. Rotation of the gear 96 in a counterclockwise'direction is limited by the arm 98 contacting with the bearing 89} as shown in Figure 14'- by'dotted-li'nes. Rotation in the opposite' directionzislilnitedbymovement of the bar 'lGa rocks the rocker arm 85 'which', in turn, rocks thetoggleshaft 51a. The'bar 16a and the rocker arm 85 .ward pull on bar 16a.

will be off center, even when the door 26a is seated, as shown in Figure 11, to facilitate rocking of arm 85 when a thrust is exerted on bar 16a by counterclockwise rotation of gear 96.

counterclockwise rotation of handwheel 81 will result in counterclockwise rotation of gear 96 and this will exert a rear and upward thrust on to slide rearwardly on the shaft 51a. In other words, the bar 5911 and the collar 50a carried thereby, along with the associated parts, is moved bodily rearwardly to swing the hopper rearwardly about the pivot axis 22a.

After discharge of the mixer drum contents, the door 260. is seated by rotating handwheel 81 in the opposite direction. This rotates gear 96 clockwise, causing it to exert a forward and down- This rocks the arm 85 downwardly and forwardly and rocks the toggle levers 84 in a similar direction. This exerts a forward thrust on the links 8|, moving the rod 59a and associated parts forwardly bodily and thereby swinging the hopper Ila. into charging position. As soon as the door 26a seats on the seat around the mixer drum opening, the spring movement of bar 59a, and associated parts, and

then resilient pressure is applied on the door by movement of member 5011 relative to bar 59a and against the pressure of spring 6111. Furthermore, the toggle is permitted to look by reason of the fact that spring 61a permits the pivots 83 to move downwardly beyond center.

It will be apparent that in this structure, the sealing joint 21a between door 26a and hopper I la is the same as in the previously described structure. This will permit rotation of the member 26a with themixer drum and relative to the hopper as the door is seated. The force to move the hopper between its charging and discharging positions is applied substantially at the center of the hopper which simplifies the structure. Furthermore, this ensures uniform pressure being applied around the door 260. when it is being forced into contact with its seat around the drum opening.

. It will be apparent that the hopper is mounted for movement'between charging and discharging positions without providing any obstruction to free flow of material through the hopper, the annulus or the mixer opening. Furthermore, it will be apparent that by a simple control, the hopper may be moved between its two positions.

Various other advantages will be apparent.

Having thus described our invention, what we claim is:

1. In combination with a mixer having a rotatable mixing drum with an end opening through which the material is charged and discharged, a charging device movable between charging and discharging positions, means for moving'said device between such positions and including a fluid cylinder and piston unit connected to said device and to a support carried by themixer, means connected to said unit for controlling said unit to cause it to thrust said chargingdevice into charging position, and resilient means engaging said unit and permitting limited yielding movement thereof in a direction opposite to the direction of said thrust when the charging device is moved into charging position so as to hold said charging device resiliently in charging position.

2. .In combination with a mixer having a rotatable mixing drum with an opening through which the material is charged and discharged, 2. charging device including a hopper adapted to be moved into association with said opening oraway from said opening, means for supporting said hopper on a support carried by said mixer for movement between the indicated positions, means for moving said hopper between such positions and including a fluid cylinder and piston unit which is connected to said hopper, means for supporting the cylinder and piston unit from said support, said means comprising a member carrying said cylinder for axial movement, and resilient means for resisting axial movement of said cylinder away from said hopper as said cylinder and piston unit thrusts said hopper into charging position in association with said opening.

3. A structure according toclaim 2 wherein an annular door is provided between said hopper and said drum opening, and means for rotatably mounting said door on said hopperu i. In combination with a mixer having a rotatable mixing drum with an opening through which the material is charged and discharged, a charging device including a hopper, means for mounting said hopper for vertical swinging movement towards and from said opening, said means including a pivot structure for connecting the hopper to a support on the mixer for vertical swinging movement, an annular door rotatably carried at the inner side of said hopper for cooperation with said opening, and means for swinging said hopper with the door carried thereby about said pivot structure to move the door into position over said opening or in spaced relationship to said opening, said means comprising a fluid-actuated cylinder and piston unit connected to the rear side of said hopper and to a fixed support provided on said mixer, the cylinder of said unit being mounted for axial movement in a sleeve carried by said support, and a compression spring carried in said sleeve and resisting movementof said cylinder away from said hopper.

5. A structure according to claim 4 wherein said sleeve is pivoted to said support for vertical movement and said cylinder and piston unit is pivotally connected to said hopper for vertical movement.

6. A structure according to claim 5 wherein a sealing joint is provided between said annular 

